Replacing LMV84x by AD8646/8648 ?

Hi,

We are now studying to replace LMV84x on existing system by AD8646 or AD8648, then having questions as follows.

1) Absolute Maximum Ratings of input voltage at AD8646/8648 is defined as "GND to Vsy".

  I could not find any clear definition in the datasheet what is Vsy, but assuming it has to be Supply Voltage, from analogy of Isy defined as Supply Current Per Amplifier.

  Is this true ? Correct me if wrong.

2) When using AD8646/8648 at 5V single supply, however input voltage can be the rage from  -(minus)0.3 to 0V.

  It seems out of range defined on Absolute Maximum Ratings in the datasheet, so is it not available to use, even if it is only an instant of eye blink ?

  Please make sure if it is correct.

3) LMV84x is RRin and RRout, 5V single supply but it is still available to  -(minus)0.3V input voltage.

  I looked for the same ADI parts and found AD8607/AD8609, but their GBP is around 300KHz, and we need a few MHz bandwdth.

  Could you provide other ADI parts which fullfill above conditions (R-R in, R-R out, single supply 5V,  -0.3~0V input voltage, GBP=a few MHz) ?

  Hopefully Vos (Offset Voltage) is a few handreds uV range and Ib (Bias Current) is around 1pA, not to be far outweighed by LMV84x.

Best Regards,

Usaghi

  • Hi Usaghi,


    Regarding to your first question,  you're right about Vsy and Isy. Vsy or simply Vs, is the supply voltage of the part while Isy is the supply current per amplifier of the part.


    On your second question, actually our parts has input over-voltage protection diodes. However, it is not guaranteed that the part will not be damaged from overstressing the input. That's the reason why we have limits on the spec table to ensure the performance of the part within the limits. You may also try to read this tutorial about input over-voltage protection: http://www.analog.com/media/en/training-seminars/tutorials/MT-036.pdf


    I suggest the AD8691 part. At a supply voltage of 5V, it has an input voltage range of -0.3V to 3.9V. It is a rail-to-rail output amplifier, has a GBP of 10MHz, has a typical input offset voltage of 400uV and has a typical input bias current of 0.2 pA. You may also try to look at ADA4691 part.


    Can I ask what is your application?

    I hope this helps!

    Regards,

    Jay

  • Hi Usaghi,

    I'm glad that I helped you. If you have any other concerns, kindly let me know. You can contact me through my email.

    Regards,

    Jay

  • Hi Jay,

    It was great help and instruction, that I appreciate a lot.

    I will talk this with our end customer just in this afternoon, so it was also great just in time !

    I can say about the application in closed loop, so if you let me know which way you prefer to be contacted, I will answer to.

    Thank you again for your support.

    Best Regards,

    Usaghi